There is a need for low-density porous ceramic particles as indicated, for example, by Bettis Atomic Power Laboratory's Letter of Inquiry No. WAPD-PP(CP)CC-1670 dated July 31, 1981, and attached specification. This letter of inquiry requests magnetite spheres within the range 0.25 to 1.19 millimeter in diameter, having an apparent (or bulk) density less than 2 grams/cubic centimeter, and a minimum average crush strength of 200 grams as measured by crushing individual spheres between an anvil and a load pin connected to a strain gauge and indicator.
At present, efforts have been made to meet this need with particles made by sol-gel techniques. However, the particles supplied are severely cracked and weak due to the great shrinkage involved when prepared by the sol-gel technique.